You still want to cool the wort to RT for the refractometer reading, since density will change with temperature and a hot reading will read low. Luckily, the volume is so small it cools very quickly. I pull a small amount into a dropper, set it aside for a minute (which might be overkill), then drop it onto the refractometer. I always check the refractometer a second time, after it has cooled a few seconds longer, just to make sure that the reading was taken while the temperature was stable.